Rock-piercing method and blowpipe



April 14, 1959 c. A. NAPIORSKI ROCK-PIERCING METHOD AND BLOWPIPE -Filed- Oct. 16. 1953 2 Sheets- Sheet .1

.7 INVENTOR CARL A. NAPIORSKI BY ATTORNE United States Patent ROCK-PIERCING METHOD AND BLOWPIPE Carl A. Napiorski, Glen Ridge, NJ., assignor to Union Carbide Corporation, a corporation of New York Application October 16, 1953, Serial No. 386,591

13 Claims. (Cl. 255--1.8)

The present invention relates to internal combustion type blowpipes and, more particularly, to a rock-piercing blowpipe having novel nozzle construction and operating on the internal combustion principle.

Heretofore, rock-piercing burners of the internal combustion type have been employed which produce oxyfuel exit flame jets having supersonic velocities (of approximately 4,500 to 6,500 feet per second and temperatures of about 2,500 F.3,200 F.) by operating at internal combustion chamber pressures above the critical pressure. sonic velocity flame jets of small diameter, small crosssectional area and high unit heat transfer. It has been found that flames of this type are highly desirable for thermal rock-piercing of mineral bodies which, due to their relatively high melting points, large grain structure and few extraneous material inclusions, are easily spalled, such as quartz, taconite, coarse-grained dolomite, granite and the like. On the other hand, it has been found that thermal rock piercing may be accomplished only slowly and with difficulty when working on so-called melty rock, such as copper ores, basaltic traprock and, in general, the basic igneous rocks which tend to melt rather than spall. Seamed or cracked minerals which otherwise spall also offer considerable resistance to rock piercing with supersonic flame jets such as used heretofore.

It is, therefore, the main object of the present invention to provide a blowpipe which, although employing the internal combustion advantages, generates flames suitable for the rapid and eflicient piercing of mineral bodies which are diflicult to pierce by a thermal spalling action.

Another object of the invention is to provide a blowpipe which by the easy interchangeable substitution of "burner parts may produce a flame most suitable for the thermal rock piercing of the specific kind of mineral body sought to be pierced.

Other aims and advantages of the present invention will be apparent from the following description and appended. claims.

In the drawings:

Figs. 1 and 2 are schematic views in section of blowpipe nozzles illustrating the principles of the improvements ac-- cording to the invention;

Fig. 3 is a view of a longitudinal section taken through a portion of a rock piercing blowpipe embodying one pre ferred construction according to the invention;

Fig. 4 is a view of a section of the nozzle of the blowpipe taken along the line 44 of Fig. 3;

Fig. 5 is a sectional view of the nozzle of the blowpipe taken along the line 5-5 of Fig. 3;

Fig. 6 is an exploded perspective view of the nozzle elements of the blowpipe of Fig. 3;

Fig. 7 is a. sectional elevational view of the lower portion of a blowpipe embodying another preferred construc-- tion in accordance with the invention;

Fig. 8 is a bottom view of the nozzle of the blowpipe= of Fig. 7;

Fig. 9 is a sectional elevational view of the lower por- Such operation results in the production of super-" "ice tion of still another blowpipe embodying a further preferred construction in accordance with the invention; and

Fig. 10 is a bottom view, partially broken away, of the nozzle of the blowpipe of Fig. 9.

It has been found that the inefliciency and reduced speeds encountered heretofore in flame piercing difficult to spall mineral bodies was due in a large measure to the use of a supersonic velocity jet flame. Such a flame is characteristically of small diameter and cross-sectional area and accomplishes an exceedingly high unit heat transfer to the mineral body being pierced. Consequently, when relatively low melting point minerals are sought to be pierced with such flames, slow and ineflicient piercing rates result due to the melting of these mineral bodies.

Attempts were made to produce flame jets having exit velocities at and below sonic velocity by operating blowpipe internal combustion chambers at below the critical pressure. Such attempts were unsuccessful in that the resultant flame jets discharged from the blowpipe were not suitable for mineral piercing applications.

It was then conceived that the efiiciency of the internal combustion principle With the chambers operating at greater than critical pressure could be retained while providing nozzle flame jets having exit velocities at and below sonic velocity and of a character that provides improved piercing rates in the melty mineral bodies.

In accordance with the present invention, there is provided a novel rock-piercing blowpipe comprising a nozzle having at least one internal combustion chamber capable of operating at greater than critical pressure and a discharge path from said chamber having at least one series of alternatively diverging and converging sections of successively increasing exit areas and constructed to provide a discharge flame of high heat energy but which has subsonic velocity and is relatively diflused i.e. bushy rather than narrow and jet-like. As employed herein, the term critical pressure refers to that pressure in the combustion chamber at which gaseous combustion products, passing from the chamber through an orifice or discharge throat, attain critical flow (sonic velocity).

Fig. 1 of the drawings is a schematic view of a blowpipe burner nozzle having an internal combustion chamber C includes sections D R D R and D Sections D D and D are diverging sections, while sections R and R are converging in shape. The alternate positioning of diverging and converging sections, causes alternate expansion and compression of the hot combustion products. Throats t t and t are regions of sonic velocity; sections R and R are regions shaped to provide compression shock; sections D and D are regions of expansion acting to produce supersonic velocity; and section D is a discharge region of subsonic velocity. The successive corresponding sections have successively larger cross-sectional areas.

It has been found that, with suflicient alternate ex pansions and compressions in sections of successively in creasing exit area, combustion products issuing at greater than sonic velocity from a combustion chamber operating at greater than critical pressure can be discharged from the blowpipe to the atmosphere as a flame jet having a subsonic velocity.

The alternate compression and expansion of combustion products in a burner nozzle as shown in Fig. l is substantially equivalent to operation of a burner nozzle as shown in Fig. 2 wherein the discharge path from chamber C comprises a series of combustion chambers C and C separated by diverging throat sections of successively increasing cross-sectional area. A comparison of the burner nozzle of Fig. 2 with that of Fig. 1 is facilitated by consideration of the dotted line structure superimposed in Fig. 2. In effect, the series of diverging-converging sections of Fig. 1 may be considered equivalent to a series of hypothetical chambers CH CH etc. interconnected by diverging sections as shown in Fig. 2.

It has been found that there is a reduction in velocity of combustion products of the order of about 35% between successive throat sections t t and t i.e. t =0.65t t =(0.65) t It can be seen that for any given number of successive diverging-converging sections the final throat velocity will be approximately:

where V is the velocity in the region of throat t into which combustion chamber C discharges, and V is the velocity in the region of the final throat t Hence if, for greater than critical pressure operation of combustion chamber C the velocity in the diverg ing section downstream of t is supersonic and about 600 f.p.s., two diverging-converging sections described hereinabove would be required to lower the velocity to a value of about 2500 f.p.s. which is below the sonic velocity in the burning gases at the temperatures concerned (about 3000-3300 f.p.s.). Should the velocity in the region downstream of be only slightly above sonic velocity it would require only one diverging-converging section as described hereinabove to accomplish a reduction to below the sonic velocity.

Referring more specifically to the embodiment shown in Figs. 3-6 of the drawings, a cylindrical steel sleeve S encloses longitudinal tubes and K for supplying oxidizing gas and fuel, respectively to the nozzle N. Sleeve S provides an annular space 17 for the passage of cooling water through the blowpipe and extends forwardly over nozzle N to a position a short distance in back of the nozzle front end. Longitudinally extending radial teeth X and X on the outside of sleeve S project forwardly therefrom to a position about even with the front end of nozzle N for grinding up and disintegrating detritus and for sizing a hole. Drag on the sides of a hole is reduced, with a commensurate increase in piercing rate, by having alternate teeth X about the same length as the sleeve S, and the other teeth X about half that length; and by having the rear ends of the long teeth X lying on a circle of slightly smaller diameter than the circle upon which the front ends lie. The difference in diameter can be elfected by a gradual taper, or by steps. Nozzle N is desirably formed of metal having high thermal conductivity in order to insure proper cooling.

The tubes K and O, and a third longitudinal tube (not shown) which serves to enclose water in the annular space 17 within the upper portion of sleeve S, extends rearwardly to a swing joint (not shown) which may be of the type disclosed and claimed in US. Patent 2,628,- 817 issued February 17, 1953, to Ray 0. Wyland. Such a swing joint supplies fuel oxidizing gas and water to the respective tubes while permitting the tubes, the sleeve S, and the nozzle N to all rotate as a unit during the piercing of a hole in a mineral body.

The nozzle N includes a cylindrical header 11, only the lower portion of which is shown in the drawing. Cooling water passes through the annular space between sleeve S and nozzle N.

Two parallel longitudinal bores 19 and 21 extend down from the top of header 11 for receiving the fuel and oxygen supply tubes K and 0, respectively. An eccentrically arranged oxygen duct 23 leads from bore 21 to an orifice in the front face of header 11. A fuel duct 25 leads from bore 19 to an axially arranged conical seat 26 in the front face of header 11, and includes a threaded internal portion 27.

Nozzle N also includes a coupling sleeve 29 threaded over the lower portion of header 11 and having a series of radially arranged radial water ducts 31 extending therethrough below the header.

A hollow atomizer body 33 comprises a cylindrical rear portion 35 fitting within coupling sleeve 29 and secured tightly thereto, as by a silver soldered joint 37, and a front portion 39 flaring forwardly from sleeve 29 and terminating at its front end in an annular shoulder 40 which engages at its outer edge the inside wall of the sleeve S. The interior of atomizer 33 comprises a cylin drical axial entrance bore 41 opening at its rear end into a conical axial rear counterbore42 which engages a conical external shoulder 43 on the front end of header 11 and opening at its front end into a large conical axial front counterbore 45 which is symmetrical about the longitudinal axis of the nozzle and forms the rear portion of combustion chamber C A fuel injector F extends into the atomizer 33. The tapered conical shape of counterbore 45 reduces erosion by combustion gases to a minimum and increases chamber life over previous blowpipes.

Cooling of atomizer 33 is accomplished by passing water from annular space 17 through radial ducts 31 into an annular water-distributing passage 47 surrounding bore 41. Passage 47 is formed by an annular external groove in the cylindrical atomizer portion 35 which registers with ducts 31. Water is conducted thence through a series of circumferentially arranged equally spaced bores 49 in the frusto-conical front portion 39 which extend parallel and close to the wall of counterbore 45 and terminates in orifices in the annular shoulder 40.

The intermediate portion of nozzle N comprisesmernber 51 which has an annular rear shoulder 53 engaging the inner edge of atomizer shoulder 40 and secured thereto, as by silver soldering at 55. From shoulder 53, member 51 extends forwardly in spaced relation to the inner wall of sleeve S to a forwardly facing annular shoulder 57 which defines, with the shoulder 40, an an nular space 59 for receiving cooling water from the bores 49. In addition to the supply of cooling water contained in annular space 59, a series of circumferentially-arranged water bores 60 pass internally through the length of intermediate nozzle member 51 and terminate in orifices in the annular shoulder 61 of frusto-conical front portion 62 of member 51.

Intermediate nozzle member 51 is provided with a hemispherical cavity 63 at its rear end which is symmetrical about the axis of nozzle N and which cooperates with and joins smoothly with counterbore 45 of frustoconical front portion 39 of atomizer 33 to form a first combustion chamber C Cavity 63 could alternately have any other suitable shape, such as paraboloidal, ellipsoidal or conical. The cavity 63 constitutes a converging passage which merges at a throat 98a with a diverging passage 68. The latter passage is joined by a converging passage 70 to form a chamber C which opens into a second throat 93b which preferably extends over an apprcciable length at a substantially constant cross-sectional area and opens into a second diverging counterbore 64 which at the downstream end of member 51 terminates in a mouth preferably having the same diameter as the mouth of counterbore 45.

The nozzle tip member 65 is provided with an annular rear shoulder 67 adapted to engage the inner edge of annular shoulder 61 of member 51 and secured thereto, as by silver soldering at 69. From shoulder 67, the tip member 65 extends forwardly and outwardly to the inner Wall of sleeve S to form a shoulder 71 which with shoulder 61 defines an annular external groove 72 for receiving the cooling water discharged from bores 60. The tip member 65 extends forwardly from shoulder 71 as a cylindrical section 73 which closely engages the inner wall of sleeve S, and projects forwardly therefrom.

Nozzle tip member 65 is provided at its rear end with a hemispherical cavity 74 which is symmetrical about the axis of nozzle N and which cooperates with and joins smoothly with counterbore 64 of intermediate member 51 to form a third combustiton chamber C Cavity 74 could alternatively have any other suitable shape, such as paraboloidal, ellipsoidal or conical which permits a streamline flow of combustion gases. The forward end of tip member 65 comprises a flat central end surface 75 normal to the axis of the blowpipe, surrounded by frustoconical beveled surface areas 76 and 76a. Positioned at surfaces 75 and 760: are two orifices through which diverging passages P and P communicating with chamber and separated therefrom by throats 98c and 98d respectively, discharges flames from the forward end of nozzle N. Diverging passage P is eccentrically displaced from and parallel to the longitudinal axis of nozzle N while diverging passage P is forwardly positioned at an acute angle to the longitudinal axis of nozzle N.

Annular gaskets, such as rubber 0 rings, are provided between portions of nozzle N and the inner wall of sleeve S to establish and maintain proper cooling water distribution around and through the nozzle. Thus, gasket 80 is provided in annular space 81 of atomizer body 33 to form a water-tight seal, gasket 82 is provided in annular space 83 of intermediate nozzle member 51 and gasket 84 in annular space 85 of tip member 65.

Since nozzle tip member 65 is subject to very high temperatures during the operation of the blowpipe it is essential that a network of water circulating passages be provided therein and that cooling water be' circulated at high velocity. A series of longitudinal drillings 86 are provided around the outer flange of member 65 in the region near the throat sections P and P These drillings are supplied with cooling water from annular groove 72 and communicate with and discharge water through radial ports 87 positioned at the lower end of tip member 65 below the lower end of sleeve S. Similarly, drillings 88 pass radially from annular groove 72 to the bore 89 formed by a drilling in the flat surface 75, closed by a cylindrical metal plug 90 which fits within bore 89 and is secured as by soldering at 91. Cooling water passes from bore 89 through radial drillings 92 to ports, similar to ports 87, positioned on the outer surface of the lower end tip member 65. Ports 87 and 92 are desirably either normal to the longitudinal axis of the blow pipe, or inclined slightly rearwardly and outwardly. The water emanating from such ports quenches the detritus and renders it more friable for disintegration, and is then vaporized to steam by the heat of the flame and acts in concert with the gaseous products of combustion to eject particles of detritus from the hole being pierced in the mineral body.

A combustible mixture can be introduced through the cylindrical bore or entrance 41 into combustion chamber C in any desired way. However, it has been found especially advantageous to direct a ring of longitudinally flowing oxygen streams at high velocity toward the chamber while concurrently directing into the oxygen streams from within the ring a plurality of radial streams of liquid fuel, such as kerosene, flowing substantially normally to the oxygen streams. The latter streams shear off and atomize the liquid fuel streams to form a combustible mixture which is then injected into the combustion chamber and burned. Injecting the fuel in a number of jets increases the surface area available for atomization and this, coupled with the shearing action of the oxygen streams, improves mixing and fuel utilization over previous procedures.

The foregoing method of operation is accomplished by supplying liquid fuel from the header duct 25 to an axial longitudinal bore 94 in the fuel injector F which is threaded into the front portion 27 of duct 25 and has an external conical portion 95 positioned against seat 26 in header 11. Bore 94 terminates short of the front end of injector F and fuel is discharged therefrom through a series of equispaced radial ports 96 whose outer ends severally open into a plurality of longitudinal grooves formed between longitudinal lands 97 which fit snugly within the cylindrical nozzle bore 41. While only one radial port has been shown as entering each groove, it is apparent that more ports can be used. The injector can 6 be operated successfully without lands 97, so that the fuel is discharged into an annulus.

In operation, the blowpipe of the present invention provides flame jets having characteristics which are ideally suited for the thermal piercing of hitherto diflicult to spall minerals. The flame jets from a blowpipe in accordance with the invention are below sonic velocity (about 3000-3300 feet per second) and are characterized by their bushy (large diameter) appearance and low unit heat transfer. It is believed that it is the low unit heat transfer and lower velocity which permits this piercing of so-called melty rock without the extreme melting encountered when blowpipes providing supersonic velocity jets are employed.

The velocity of combustion products is sonic in the region of throat 98a and supersonic in the divergent section 68 of chamber C In this chamber the gases are expanded and then suddenly recompressed in convergent section 70. They are then discharged through throat 98b into chamber C where further expansion and recompression is accomplished before discharging through throats 98c and 98d to passage P and P respectively.

It has been found that a continually increasing exit area is encountered at each stage of expansion, i.e. the exit area increases for each successive section in which the combustion products are allowed to expand. Thus, the exit area at point 98b of chamber C is greater than the inlet area at point 98a; and the exit area of chamber C which equals the sum of the areas of throats 98c and 98d, is greater than the inlet area of chamber C which is the area of 98b. The net result is a reduction in velocity from supersonic velocity in the diverging portion 68 of chamber C to a subsonic velocity as the flame or flames emanate from the final passage or passages to the atmosphere. This reduction in velocity is accompanied by the other desirable factor, namely a flame jet of greater diameter. A flame jet having both of these characteristics will be successful in piercing so-called melty rock, as discussed hereinabove.

The present invention is not limited to a blowpipe construction as shown in Figs. 3 to 6 of the drawings. Another modification of a blowpipe embodying the invention is shown in Figs. 7 and 8 of the drawings. As there shown, a blowpipe similar to that of Figs. 3 to 6 is shown having three flame jets, and elements of this embodiment have been assigned identical numerals increased by 100, where they correspond to equivalent elements of the embodiment of Figs. 3 to 6. Similarly, the embodiment shown in Figs. 9 and 10 of the drawings is similar to that shown in Figs. 3 to 6 except that a single combustion chamber is employed discharging into two separate and relatively divergent series of multiple chamber sections. As there shown, elements of this embodiment correspond to the equivalent elements of the embodiment of Figs. 3 to 6 which have been assigned numerals increased by 200.

It was found, when developing the embodiment of the invention shown in Figs. 9 and 10 of the drawing, that a long series of alternate diverging-converging sections such as chamber C C and C of Fig. 9, is in effect the equivalent of a series of hypothetical chambers and connecting throat sections as shown in Fig. 2. The effect on combustion products is substantially the same and a desired subsonic bushy jet flame is discharged as long as the series of throat sections are of the proper increasing areas in the downstream direction.

It is to be understood that the expansion ratio obtainable in a given diverging-converging throat section has an upper and a lower limit. For a given throat section having an inlet area=A and an exit area=A the expansion ratio (E.R.) may be expressed as:

The expansion ratio should be maintained below a 7 value at which the fluid is expanded to about atmospheric pressure since the wave front will collapse where the ratio is too great. Conversely, the expansion ratio should not be so low a value that the fluid stream is not expanded sufficiently.

In addition, for efficient operation, it is necessary that the discharge orifice from each combustion chamber be properly constructed. The L-star ratio, which is the ratio of chamber volume in cubic inches to the total discharge orifice area in square inches, must be within such a range as will permit efficient nozzle characteristics.

The nozzles of the present invention are short and will effect a reduction in effective pressure by factor of two, three, four, or even more depending on the number of throat sections employed. The effect is, therefore, the production of subsonic velocities from combustion or pressurized chambers having pressures greatly in excess of critical pressure in a nozzle-which is relatively short.

In the jet motor art it is at times desirable to obtain a reduction in the velocity of a gaseous fluid jet. Heretofore, such velocity reduction had been accomplished by various means, such as diffuser sections. Such means are of unduly great length and pressure differentials of only about 2:1 (maximum) are involved.

Velocity reduction in accordance with the present invention may be accomplished with compact apparatus and reductions in effective pressure greater than 4:1 are attainable if a suitable number of throat sections are employed.

In one example, a 6 inch O.D. blowpipe of the type shown in Figs. 3 to 6 of the drawings, employing an oxygen and kerosene fuel mixture pierced a series of vertical holes having a depth greater than 200 feet in taconite at speeds averaging 17.5 feet per hour and at times as high as 25 feet per hour.

In another example, a so-called melty traprock known as Kingston traprock was pierced at a speed averaging about 20 feet per hour with a 6 inch O.D. blowpipe embodying the invention and employing an oxykerosene fuel mixture.

It has been found that a series of interchangeable nozzles may be provided each capable of delivering from a blowpipe a sub-sonic flame jet having characteristics which are ideal for use in the thermal piercing of a particular type of mineral body. In that manner, nozzles may be substituted in the blowpipe depending on the type of flame jet most suitable in producing the best result in a given operation.

What is claimed is:

1. A mineral piercing blowpipe having an elongated body, inlet means for fuel, oxidant and water positioned near one end thereof, a nozzle member positioned at the other end thereof, and conduit means in said body extending from said inlet means for separately supplying said fuel, oxidant and Water to said nozzle member; said nozzle member containing at least two internal chambers connected in series and disposed from the rear end toward the forward end thereof, and at least one diverging passage at said forward end communicating with the most forwardly disposed of said chambers for dis charging combustion products from said series of chambers, wherein at least the most rearwardly disposed of said chambers is an internal combustion chamber with means for providing a combustion therein at greater than critical pressure and said chambers and said diverging passage are connected by throat sections, said throat sections being of increasingly greater cross-sectional area in the direction from the rear to the forward end of said nozzle; said blowpipe also containing conduit means for passing said water therethrough successively around each of said chamber walls and throat sections and terminating in said nozzle in water discharge port means positioned on an external surface thereof for discharging water from said nozzle member in the region of discharge of flame from said nozzle member.

2. A blowpipe in accordance with claim 1, wherein said throat sections comprise a region of constant crosssectional area anda diverging region of increasing crosssectional area positioned forwardly of said region of constant cross-sectional area.

3. A mineral working blowpipe having an elongated body, inlet means for fuel, oxidant and water positioned near one end thereof, a nozzle member positioned at the other end thereof, and conduit means in said body extending from said inlet means for separately supplying said fuel, oxidant and water to said nozzle member; said nozzle member containing at least two internal chambers connected in series and disposed from the rear end toward the forward end thereof, and at least one diverging passage at said forward end communicating with the most forwardly disposed of said chambers for discharging combustion products from said series of chambers, wherein at least the most rearwardly disposed of said chambers is an internal combustion chamber with means for providing a combustion therein at greater than critical pressure and said chambers and said diverging passage are connected by throat sections, said throat sections being of increasingly greater cross-sectional area in the direction from the rear to the forward end of said nozzle member; said blowpipe also containing conduit means for passing said water therethrough successively around each of said chamber walls and throat sections and terminating in said nozzle in water discharge port meanspositioned on an external surface thereof for discharging water from said nozzle member in the region of discharge of flame from said nozzle member.

4. A blowpipe in accordance with claim 3, wherein said throat sections comprise a region of constant crosssectional area and a diverging region of increasing crosssectional area positioned forwardly of said region of constant cross-sectional area.

5. A blowpipe in accordance with claim 3, wherein at least one combustion chamber other than said most rearwardly disposed of said chambers is diverging-converging in shape and of increasing cross-sectional exit area in the direction from the rear to the forward end of said nozzle.

6. A blowpipe in accordance with claim 3, wherein all of said combustion chambers other than said most rearwardly disposed of said chambers are diverging-converging in shape and of increasing cross-sectional exit area in the direction from the rear to the forward end of said nozzle.

7. A blowpipe in accordance with claim 6 having at least three combustion chambers wherein said combus- 'tion chambers other than said most rearwardly disposed of said chambers are positioned and arranged to form at least two separate and relatively divergent discharge paths from said most rearwardly disposed of said chambers.

8. A mineral working blowpipe having an elongated body, inlet means for fuel, oxidant and water positioned near one end thereof, a nozzle member positioned at the other end thereof, and conduit means in said body extending from said inlet, means for separately supplying said fuel, oxidant and water to said nozzle member; said nozzle member containing at least two internal chambers connected in series and disposed from the rear end to ward the forward end thereof, and at least one diverging passage at said forward end communicating with the most forwardly disposed of said chambers for discharging combustion products from said series of chambers, wherein the most rearwardly disposed of said chambers is an internal combustion chamber with means for introducing therein a pre-mixed stream of gaseous oxygen and fluid fuel for providing combustion therein at greater than critical pressure, said chambers and said diverging passage being connected by throat sections, said throat sections being of increasingly greater cross-sectional area in the direction fromthe rear to the forward end of said nozzle; said blowpipe also containing conduit means for passing said water therethrough successively around each of said chamber walls and terminating in said nozzle in Water discharge port means positioned on an external surface thereof for discharging water from said nozzle member in the region of discharge of flame from said nozzle member.

9. A method for producing flame jets having exit velocities below sonic velocity and issuing from an internal combustion chamber rock-piercing blowpipe having at least one enclosed combustion zone operating at above critical pressure comprising, introducing fluid fuel and oxidant to such zone at a rate and pressure sufiicient to effect burning of the combustible mixture therein at greater than critical pressure; discharging the resulting burning combustible mixture as a stream from such zone and constricting said stream to accelerate the mixture to sonic velocity; expanding said stream at a rate of expansion which accelerates said stream to a supersonic velocity; contracting the resulting supersonic stream of burning combustible mixture to set up shock waves which operate to brake the velocity of said stream and effect an increase in temperature of said stream; effecting said alternate expanding and contracting steps at least once and sufficient to reduce the final velocity of said stream to less than sonic velocity; and discharging the resulting stream against the material to be treated.

10. A method for producing flame jets having exit velocities below sonic velocity and issuing from an internal combustion chamber rock-piercing blowpipe having at least one enclosed combustion zone operating at above critical pressure comprising, introducing fluid fuel and oxidant to such zone at a rate and pressure sufiicient to efiect burning of the combustible mixture therein at greater than critical pressure; discharging the resulting burning combustible mixture as a stream from such zone and constricting said stream to accelerate the mixture to sonic velocity; expanding said stream at a rate of expansion which accelerates said stream to a supersonic velocity; contracting the resulting supersonic stream of burning combustible mixture to set up shock waves which operate to brake the velocity of said stream and effect an increase in temperature of said stream; effecting said alternate expanding and contracting steps as many times as is necessary to effect a net over-expansion of said stream and a final reduction in velocity of said stream to a sub-sonic velocity; and discharging the resulting stream against the mineral to be treated.

11. A method for producing flame jets having exit velocities below sonic velocity and issuing from a thermal rock-piercing blowpipe having an enclosed combustion zone operating at above critical pressure comprising, introducing fluid fuel and oxidant to such zone at a rate and pressure sutficient to effect burning and the combustible mixture therein at greater than critical pressure; discharging the resulting burning combustible mixture as a stream from such zone and constricting said stream to accelerate the mixture to sonic velocity; expanding said stream at a rate of expansion which accelerates it to a supersonic velocity; contracting the supersonic stream of burning combustible mixture to set up shock Waves which operate to brake the velocity of said stream and effect an increase in temperature; repeating said alternate expanding and contracting steps as many times as is necessary to expand said stream to reduce the velocity to less than sonic velocity; and discharging the resulting stream, thereby providing a finely, partially difiused, subsonic flame jet for thermal mineral treating.

12. In a blowpipe, a nozzle at the discharge end thereof comprising an internal combustion chamber having an inlet end, an outlet end, and means for effecting combustion therein at greater than critical pressure; means providing at least a first constricted orifice positioned at the outlet end of said internal combustion chamber for accelerating the stream of burning combustible mixture discharged from said chamber to sonic velocity; means having walls providing at least one discharge path from said internal combustion chamber communicating with said first constricted orifice and comprising at least one series of alternate diverging and converging discharge passages for alternately expanding and contracting the stream of burning combustible mixture discharged from said internal combustion chamber, and at least a second constricted orifice communicating with the lower end of said converging discharge passages and having the same cross-sectional area as said lower end; and an exit diverging discharge passage communicating with the lower end of each of said discharge paths for discharging said stream of burning combustible mixture from said blowpipe; said first orifice, the second orifice of said discharge path, and exit passage being of increasingly greater cross-sectional area in the direction from said internal combustion chamber to the discharge end of said nozzle.

13. In a blowpipe, a nozzle at the discharge end there of comprising an internal combustion chamber having an inlet end, an outlet end, and means for effecting combustion therein at greater than critical pressure; means providing at least two first constricted orifices positioned at the outlet end of said internal combustion chamber for accelerating the streams of burning combustible mixture discharged from said chamber to sonic velocity; means having Walls providing at least two discharge paths from said internal combustion chamber, each communieating with one of said first constricted orifices and comprising at least one series of alternate diverging and converging discharging passages for alternately expanding and contracting a stream of burning combustible mixture discharged from said internal combustion chamber and at least a second constricted orifice communicating with the lower end of each of said converging discharge passages and having the same cross-sectional area as said lower end; and an exit diverging discharge passage communicating with the lower end of each of said discharge paths for discharging said stream of burning combustible mixture from said blowpipe; said first orifices, the second orifices of said discharge paths, and exit passages being of increasingly greater cross-sectional area in the direction from said internal combustion chamber to the discharge end of said nozzle.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,612 Wills June 6, 1933 2,327,508 Craig Aug. 24, 1943 2,375,180 Vigo May 1, 1945 2,523,656 Goddard Sept. 26, 1950 2,628,817 Wyland Feb. 17, 1953 2,675,993 Smith Apr. 20, 1954 2,738,162 Aitchison May 13, 1956 FOREIGN PATENTS 189,725 Germany Nov. 11, 1905 254,966 Great Britain July 15, 1926 

